Mourners flooded the streets of Tehran as funeral ceremonies for Iran's supreme leader Ali Khamenei officially began on Saturday, amid chants of 'death to America!' over his killing.Iranian authorities say they anticipate between 15 and 20 million participants in the capital alone over the next three days for tributes to the man who ran the country for 36 years.Six days of funeral ceremonies are planned to commemorate Khamenei, who ruled the Islamic republic as its number one from 1989 until his killing aged 86 on the first day of the US-Israeli war with Iran on February 28.Intelligence analysts are likely to look for any signs of Khamenei's son and successor Mojtaba Khamenei, who was named supreme leader a week after the killing of his father but is yet to appear in public.Iran chose July 4, the 250th anniversary of the creation of the US, to begin the funeral.Thousands of mourners carrying flags and red banners - a symbol of vengeance - were seen gathering in the courtyard of Tehran's vast Grand Mosalla religious complex waiting for the arrival of Khamenei's coffin.Meanwhile billboards across the city bore Khamenei's image.Crowds of men rhythmically beat their chests in mourning, a common practice at Shiite funerals. When it arrived, authorities unveiled the casket containing Khamenei's body in a glass case. Mourners wept at the sight, with some chanting 'death to America' and 'our word is one! Revenge! Revenge!' Some mourners were reported to have walked several kilometres to reach the venue. Hundreds of supporters of the Islamic republic were already waiting on Friday evening outside the Grand Mosalla. Mourners flooded the streets of Tehran as funeral ceremonies for Iran's supreme leader Ali Khamenei officially began on Saturday Thousands of mourners carrying flags and red banners - a symbol of vengeance Crowds gathered in the courtyard of Tehran's vast Grand Mosalla religious complex awaiting the arrival of Khamenei's coffin Thousands of Iranian women, all wearing black chadors, gathered with banners and flags The area around the complex was awash with flags and banners as the ceremony began Millions are expected by authorities to flood the streets of Tehran over the coming days A mourner carries flowers and a portrait of slain Iranian Supreme Leader Ayatollah Ali Khamenei with a child The casket containing Khamenei's body has gone on display in a glass case with his black turban atop it Other relatives killed in the strikes alongside Ayatollah Ali Khamenei will also be buried, including Ali Khamenei's infant granddaughter and Mojtaba Khamenei's late wife'I am here to say goodbye to my beloved leader Ali Khamenei,' said a weeping Hananeh Mousavi, 27, who attended the funeral alongside her mother. 'I never expected to see such a day. I wish I had died before this tragedy.' Fellow mourner Somayye Hamedi said: 'We want to say a final goodbye to our leader, which is why waiting like this isn't painful or difficult for us.' 'We attended the funeral to show that we are all committed to defend our country and religion,' said Ali Kazemi, who came from the northwestern city of Tabriz, some 530 kilometers (330 miles) away from Tehran. An outdoor stage set up at the Grand Mosalla resembled the stage where Khamenei once gave his speeches at a husseiniyah at his compound in downtown Tehran. That site was destroyed in the Israeli airstrike that killed Khamenei and some of his family at the start of the Iran war on Feb. 28. The caskets of his dead family members sat beneath his, which had his black turban atop it, identifying him as a direct descendent of the Prophet Muhammad.Significant security measures have been imposed, with roads blocked and airspace expected to be closed for what is set to be the largest-scale public event in Iran since the burial of Khamenei's predecessor Ruhollah Khomeini in 1989. Six days of funeral ceremonies are planned to commemorate Khamenei, who ruled the Islamic republic as its number one from 1989 until his killing aged 86 on the first day of the US-Israeli war with Iran on February 28 The funeral ceremonies began on Saturday at the grand Mosalla Mosque in Tehran Mourners chanted and held up banners calling for 'revenge' and 'death to America!' A woman holds up an image of US President Donald Trump with a target and the words 'there will be blood' in a call for revenge over Khomeini's killing Some mourners were reported to have walked several kilometres to reach the venue The funeral is set to be the largest-scale public event in Iran since the burial of Khamenei's predecessor Ruhollah Khomeini in 1989 Mourners were seen holding their heads and beating their chests during the farewell ceremonyThe coffin will lie in state until Monday, when a procession will pass through Tehran. On Tuesday it will move to the clerical hub of Qom, before moving on Wednesday to cities holy to Shia Muslims in neighbouring Iraq, then proceeding for burial on Thursday in Khamenei's home city of Mashhad in northeastern Iran.Officials who survived the war showed their grief and displayed a united front on Friday, with parliament speaker and top negotiator in the US talks Mohammad Bagher Ghalibaf visibly tearful.Top Iranian officials paying their respects included Ahmad Vahidi, who was named chief of the powerful Revolutionary Guards after his predecessor was killed in the same strikes that killed Khamenei but had not been seen since.The coming days will be closely watched for signs of Mojtaba Khamenei, who has communicated only by written statements and is said to have been wounded in the same strikes, though the extent of his injuries was never made clear.Other relatives killed in the strikes will also be buried, including Ali Khamenei's infant granddaughter and Mojtaba Khamenei's late wife.International guests paying respects on Friday included Pakistani Prime Minister Shehbaz Sharif, whose country has been mediating between Iran and the US, and Russian ex-president Dmitry Medvedev, now deputy head of the Russian security council, who attended on behalf of President Vladimir Putin. International guests paying respects on Friday included Russian ex-president Dmitry Medvedev, now deputy head of the Russian security council, who attended on behalf of President Vladimir Putin Pakistani Prime Minister Shehbaz Sharif, whose country has been mediating between Iran and the US, was also in attendance at a farewell ceremony on Friday The Taliban government in Afghanistan was also represented at Friday's ceremony Turkish representatives, including Vice President Cevdet Yilmaz, (centre) also attended Palestinian militant group Hamas and Lebanese Shia group Hezbollah, both backed by Tehran, were also represented, as was the Taliban government in Afghanistan.After five weeks of fighting, the Middle East conflict is on hold following an initial accord between Iran and the US. But Iranian officials have warned Tehran is ready to resume fighting if needed.'The nation's call for vengeance must ring in the ears of the whole world,' said Ghalibaf, who urged Iranians to turn out en masse.Army chief Amir Hatami vowed Israel and the US 'will pay for the blood of the martyred leader and all the nation's martyrs'.But authorities will also want the event to go smoothly, deeply aware of the risk of crowd crushes, which have marred similar events in the past, with TV broadcasting guidelines on how to stay safe.With temperatures well over 35 degrees Celsius (95 degrees Fahrenheit) expected over the next few days in Tehran, tankers were stationed to spray water on the roads to cool down attendees.Ahead of the ceremonies, media sources reported that Tehran was quieter than usual with many normally busy streets free of the capital's notorious traffic.As the official mourning period began, US President Donald Trump gave a speech in South Dakota in front of Mount Rushmore.'We knocked the hell out of Iran', he began. 'They want to settle so badly. We gave them a week off for a funeral.'The American president was not forgotten in Tehran. In the crowd in Grand Mosalla, several mourners held a large flag that read: "#KillTrump."Meanwhile Israel's repeated threats to kill Mojtaba Khamenei drew a warning from Iran's joint military command Thursday, which told Israel and the US 'to avoid any miscalculation' over the coming days.